VHF står för "Very High Frequency" och är ett frekvensband som ligger i området 30 - 300 MHz. Maritim VHF är standard för Sjöfartsverket och fungerar över hela världen. Det är ett kommunikationssystem som bidrar till ökad säkerhet och kan rädda liv på sjön. Andra vanliga kommunikationssystem som mobiltelefoni fungerar inte tillförlitligt. Idag fungerar mobiltelefoni i stora delar av skärgården och längs kusterna men när det gäller kommunikation mellan fartyg längre ut till havs är den maritima VHF-kommunikationen överlägsen. Sjöfartsverket driver för sitt eget och kunders behov ett mobilradionätverk kallat kustradionätverket. Radiotrafiken i nätet sker både på Very High Frequency (VHF) och Medium frequency (MF). VHF-systemet är ett internationellt system som bland annat används till att kommunicera till sjöss och den trafiken befinner sig i frekvensbandet 155.5 - 162.025 MHz. Inom VHF-bandet finns det 55 kanaler. Kanalerna vid kustradiostationen kallas för duplexkanaler och innebär att kustradiostationerna sänder och tar emot signaler på två olika frekvenser. Radioutbredningen hos antennen som är installerad på basstationen har riktverkan i vissa riktningar och dämpningar i andra. Detta kan ses i strålningsdiagrammet under kapitlet "Täckningsmodell" och avsnittet antennen. Andra faktorer som kan påverka radioutbredningen är förluster i basstationenssystemet, topologin hos området mellan sändare och mottagare samt väderberoende utbredningsegenskaper. Genom att hitta de tänkbara faktorer som påverkar signalutbredningen kan en täckningsmodell förutses. Det är förluster som finns i basstationen, radiolänken samt förluster vid mottagarantennen.

Στόχος της παρούσας διπλωματικής εργασίας είναι η ηλεκτρομαγνητική μοντελοποίηση υπό βρoχόπτωση στις VHF και UHF περιοχές συχνοτήτων. Προκειμένου να εξαχθούν συμπεράσματα για την ποιότητα των παρεχόμενων υπηρεσιών (κυτταρική και δορυφορική τηλεφωνία, μετάδοση τηλεοπτικών σημάτων) προσδιορίζονται η ισχύς λήψης και μία σειρά από παραμέτρους. / The aim of this master thesis is the RF modeling during rainfall for the VHF and UHF ranges. In order to infer conclusions for the quality of the supplied services (cellular and satellite telephony, transmission of television signals) the received power and a series of parameters are defined.

No description available.

No description available.

Thin-film silicon tandem solar cells based on a hydrogenated amorphous silicon (a-Si:H) top-cell and a hydrogenated microcrystalline silicon (μc-Si:H) bottom-cell are a promising photovoltaic technology as they use a combination of absorber materials that is ideally suited for the solar spectrum. Additionally, the involved materials are abundant and non-toxic which is important for the manufacturing and application on a large scale. One of the most important factors for the application of photovoltaic technologies is the cost per watt. There are several ways to reduce this figure: increasing the efficiency of the solar cells, reducing the material consumption and increasing the throughput of the manufacturing equipment. The use of very-high frequencies has been proven to be beneficial for the material quality at high deposition rates thus enabling a high throughput and high solar cell efficiencies. In the present work a scalable very-high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique for state-of-the-art solar cells is developed. Linear plasma sources are applied which facilitate the use of very-high frequencies on large areas without compromising on the homogeneity of the deposition process. The linear plasma sources require a dynamic deposition process with the substrate passing by the electrodes in order to achieve a homogeneous deposition on large areas. State-of-the-art static radio-frequency (RF) PECVD processes are used as a reference in order to assess the potential of a dynamic VHF-PECVD technique for the growth of high-quality a-Si:H and μc-Si:H absorber layers at high rates. In chapter 4 the influence of the deposition process of the μc-Si:H i-layer on the solar cell performance is studied for static deposition processes. It is shown that the correlation between the i-layer growth rate, its crystallinity and the solar cell performance is similar for VHF- and RF-PECVD processes despite the different electrode configurations, excitation frequencies and process regimes. It is found that solar cells incorporating i-layers grown statically using VHF-PECVD processes obtain a state-of-the-art efficiency close to 8 % for growth rates up to 1.4 nm/s compared to 0.53 nm/s for RF-PECVD processes. The influence of dynamic deposition processes on the performance of μc-Si:H solar cells is studied. It is found that μc-Si:H solar cells incorporating dynamically grown i-layers obtain an efficiency of 7.3 % at a deposition rate of 0.95 nm/s. There is a small negative influence of the dynamic deposition process on the solar cell efficiency compared to static deposition processes which is related to the changing growth conditions the substrate encounters during a dynamic i-layer deposition process. The changes in gas composition during a dynamic i-layer deposition process using the linear plasma sources are studied systematically using a static RF-PECVD regime and applying a time-dependent gas composition. The results show that the changes in the gas composition affect the solar cell performance if they exceed a critical level. In chapter 5 dynamic VHF-PECVD processes for a-Si:H are developed in order to investigate the influence of the i-layer growth rate, process parameters and deposition technique on the solar performance and light-induced degradation. The results in this work indicate that a-Si:H solar cells incorporating i-layers grown dynamically by VHF-PECVD using linear plasma sources perform as good and better as solar cells with i-layers grown statically by RF-PECVD at the same deposition rate. State-of-the-art stabilized a-Si:H solar cell efficiencies of 7.6 % are obtained at a growth rate of 0.35 nm/s using dynamic VHF-PECVD processes. It is found that the stabilized efficiency of the a-Si:H solar cells strongly decreases with the i-layer deposition rate. A simplified model is presented that is used to obtain an estimate for the deposition rate dependent efficiency of an a-Si:H/μc-Si:H tandem solar cell based on the photovoltaic parameters of the single-junction solar cells. The aim is to investigate the individual influences of the a-Si:H and μc-Si:H absorber layer deposition rates on the performance of the tandem solar cell. The results show that a high deposition rate of the μc-Si:H absorber layer has a much higher potential for reducing the total deposition time of the absorber layers compared to high deposition rates for the a-Si:H absorber layer. Additionally, it is found that high deposition rates for a-Si:H have a strong negative impact on the tandem solar cell performance while the tandem solar cell efficiency remains almost constant for higher μc-Si:H deposition rates. It is concluded that the deposition rate of the μc-Si:H absorber layer is key to reduce the total deposition time without compromising on the tandem solar cell performance. The developed VHF-PECVD technique using linear plasma sources is capable of meeting this criterion while promoting a path to scale the processes to large substrate areas.

Diese Arbeit beschäftigt sich mit den wesentlichen Aspekten der Hochrateabscheidung von amorphen (a-Si:H) und mikrokristallinen (μc-Si:H) Silizium-Schichten und Solarzellen. Die neuartige plasmaunterstützte chemische Gasphasenabscheidung unter Anwendung von den sehr hohen Anregungsfrequenzen bis 140 MHz (VHF-PECVD) wurde demonstriert. Die durchgeführten Untersuchungen befassten sich hauptsächlich mit der Anpassung der Anlagentechnik für den VHF Bereich und der Entwicklung des hochproduktiven Herstellungsverfahrens ohne Einbußen bei den Schichteigenschaften und dem Solarzellenwirkungsgrad. Durch Frequenzerhöhung bis 140 MHz wurde eine Steigerung der i-Schicht-Abscheiderate von 70 % sowohl für a-Si:H als auch für μc-Si:H realisiert. Die Weiteroptimierung des Solarzellenaufbaus zeigt die hervorragende Eignung des Herstellungsprozesses für die Abscheidung von hocheffizienten Solarzellen (ca. 10,7 % für a-Si:H- und 9,5 % für μc-Si:H-Zellen). Der neuartige VHF-PECVD-Prozess wurde außerdem für die Abscheidung von den Passivierungsschichten für die Silizium-Heteroübergangs-Solarzellen (HIT) getestet. Die Arbeit im VHF-Bereich ermöglicht einen Einsatz von hohen Depositionsraten bis 1 nm/s ohne Einbußen bei den Passivierungseigenschaften (2 ms Lebensdauer) im Vergleich zum 13,56-MHz-Prozess (0,5 ms Lebensdauer). Zuletzt wurde eine Analyse der Zusammenhänge zwischen Anregungsfrequenz, Plasmaleistung, Ionenenergie, Ioneneindringtiefe und Defektbildung in den intrinsischen Dünnschichtsiliziumschichten durchgeführt.:I. Abkürzungs- und Symbolverzeichnis vii 1 Einleitung 1 2 Physikalische und technologische Grundlagen 7 2.1 Plasmaunterstützte chemische Gasphasenabscheidung 7 2.1.1 Prozessparameter 9 2.1.2 Frequenzeinfluss 10 2.2 Amorphes und mikrokristallines Silizium 14 2.2.1 Eigenschaften von Dünnschichtsilizium 15 2.2.2 Siliziumbasierte Dünnschichtsolarzellen 20 2.2.3 Siliziumbasierte Solarzellen mit Heteroübergang 21 3 Entwicklung des Abscheidungsprozesses bis 140 MHz 23 3.1 Herstellung von dünnen Siliziumschichten 23 3.1.1 VHF-PECVD-Durchlaufanlage mit linearen Elektroden 24 3.1.2 F&E-Testanlage 25 3.2 Anpassung des Abscheidungssystems für sehr hohe Frequenzen 26 3.2.1 Temperaturregelung der HF Elektrode 26 3.2.2 Kompensation des Tiefpassverhaltens 28 3.2.3 Leistungseinkopplung 31 3.3 Homogenität der VHF-Abscheidung 32 3.4 Charakterisierung von dünnen Siliziumschichten und Solarzellen 34 3.4.1 Leitfähigkeitsmessung 34 3.4.2 Transmissionsmessungen im UV-VIS-NIR-Bereich 35 3.4.3 Fourier-Transform-Infrarotspektroskopie 37 3.4.4 Raman-Spektroskopie 38 3.4.5 Solarzellencharakterisierung 39 3.4.6 Messungen der effektiven Lebensdauer 42 3.5 Zusammenfassung der Ergebnisse 43 4 Hydrogeniertes amorphes Silizium im VHF-Bereich 45 4.1 Intrinsische a-Si:H Einzelschichten bis 140 MHz 45 4.1.1 Optische Eigenschaften 47 4.1.2 Strukturelle Eigenschaften 48 4.1.3 Elektrische Eigenschaften 51 4.2 a-Si:H-Solarzellen bis 140 MHz 52 4.2.1 Variation der Silankonzentration 53 4.2.2 Abscheiderateerhöhung durch Prozessleistung 56 4.3 Weitere Entwicklung der amorphen Silizium-Solarzellen 61 4.4 Zusammenfassung der Ergebnisse 62 5 Hydrogeniertes mikrokristallines Silizium im VHF-Bereich 65 5.1 μc-Si:H Schichten und Solarzellen – HPD-Regime 68 5.1.1 Einfluss des Prozessdruckes und der Silankonzentration bei hohen Gasflusswerten 69 5.1.2 Einfluss der Leistung bei hohen Gasflusswerten 72 5.2 μc-Si:H Schichten und Solarzellen – Frequenzerhöhung 74 5.2.1 μc-Si:H Schichteigenschaften – Vergleich 120 und 140 MHz 74 5.2.2 μc-Si:H Solarzellen – Vergleich 120 und 140 MHz 76 5.3 Weitere Entwicklung der μc-Si:H Solarzellen 78 5.4 Zusammenfassung der Ergebnisse 79 6 Passivierungsschichten für HIT-Solarzellen 81 6.1 Schichteigenschaften – Vergleich zwischen 13,56 und 140 MHz 81 6.2 H2-Plasma-Vorreinigung 84 6.3 Passivierungsschichten – Frequenzeinfluss 87 6.4 Zusammenfassung der Ergebnisse 88 7 Simulationsstudie 89 7.1 Ionenbeschussenergie 89 7.1.1 Modellübersicht – Ar-Plasma 90 7.1.2 Einfluss der Leistung und Betriebsfrequenz 91 7.2 Simulation des Ionenbeschusses 92 7.2.1 TRIM–Simulationssoftware 92 7.2.2 Ionenbeschuss auf die a-Si:H-Oberfläche 93 7.3 Solarzellen – Defekte in der i- Schicht 94 7.3.1 ASA–Simulationssoftware 95 7.3.2 Parameterset 99 7.3.3 Einfluss der Defektdichte auf Solarzelleneigenschaften 101 7.4 Zusammenfassung der Ergebnisse 102 8 Zusammenfassung und Ausblick 105 II. Abbildungsverzeichnis 111 III. Tabellenverzeichnis 117 IV. Literaturverzeichnis 119 V. Veröffentlichungen 129 VI. Lebenslauf 131 VII. Danksagung 133 / The following thesis deals with the main aspects of the high-rate deposition of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon layers and solar cells. The very high frequency plasma enhanced chemical vapor deposition technique with excitation frequencies up to 140 MHz (VHF-PECVD) has been introduced. These study deals mainly with the adaptation of the deposition system for the VHF-range and the development of the highly productive manufacturing process without deterioration of the layer properties and the solar cell efficiency. An increase of the excitation frequency up to 140 MHz ensured a 70 % enhancement of the a-Si:H and μc-Si:H deposition rate. A further optimization of the solar cells shows the excellent suitability of these manufacturing process for the deposition of the highly efficient solar cells (about 10.7% for a-Si:H and 9.5% for μc-Si:H cells). The novel VHF-PECVD process has also been analyzed for the deposition of the passivation layers for the silicon heterojunction solar cells (HIT). Working in the VHF-range allows the use of very high deposition rates up to 1 nm/s, without deterioration of the passivation properties (2 ms lifetime) compared to the 13.56 MHz process (0.5 ms lifetime). Finally, an analysis of the correlations between excitation frequency, plasma power, ion energy, ion penetration depth and defect formation in the intrinsic thin film silicon layers was performed.:I. Abkürzungs- und Symbolverzeichnis vii 1 Einleitung 1 2 Physikalische und technologische Grundlagen 7 2.1 Plasmaunterstützte chemische Gasphasenabscheidung 7 2.1.1 Prozessparameter 9 2.1.2 Frequenzeinfluss 10 2.2 Amorphes und mikrokristallines Silizium 14 2.2.1 Eigenschaften von Dünnschichtsilizium 15 2.2.2 Siliziumbasierte Dünnschichtsolarzellen 20 2.2.3 Siliziumbasierte Solarzellen mit Heteroübergang 21 3 Entwicklung des Abscheidungsprozesses bis 140 MHz 23 3.1 Herstellung von dünnen Siliziumschichten 23 3.1.1 VHF-PECVD-Durchlaufanlage mit linearen Elektroden 24 3.1.2 F&E-Testanlage 25 3.2 Anpassung des Abscheidungssystems für sehr hohe Frequenzen 26 3.2.1 Temperaturregelung der HF Elektrode 26 3.2.2 Kompensation des Tiefpassverhaltens 28 3.2.3 Leistungseinkopplung 31 3.3 Homogenität der VHF-Abscheidung 32 3.4 Charakterisierung von dünnen Siliziumschichten und Solarzellen 34 3.4.1 Leitfähigkeitsmessung 34 3.4.2 Transmissionsmessungen im UV-VIS-NIR-Bereich 35 3.4.3 Fourier-Transform-Infrarotspektroskopie 37 3.4.4 Raman-Spektroskopie 38 3.4.5 Solarzellencharakterisierung 39 3.4.6 Messungen der effektiven Lebensdauer 42 3.5 Zusammenfassung der Ergebnisse 43 4 Hydrogeniertes amorphes Silizium im VHF-Bereich 45 4.1 Intrinsische a-Si:H Einzelschichten bis 140 MHz 45 4.1.1 Optische Eigenschaften 47 4.1.2 Strukturelle Eigenschaften 48 4.1.3 Elektrische Eigenschaften 51 4.2 a-Si:H-Solarzellen bis 140 MHz 52 4.2.1 Variation der Silankonzentration 53 4.2.2 Abscheiderateerhöhung durch Prozessleistung 56 4.3 Weitere Entwicklung der amorphen Silizium-Solarzellen 61 4.4 Zusammenfassung der Ergebnisse 62 5 Hydrogeniertes mikrokristallines Silizium im VHF-Bereich 65 5.1 μc-Si:H Schichten und Solarzellen – HPD-Regime 68 5.1.1 Einfluss des Prozessdruckes und der Silankonzentration bei hohen Gasflusswerten 69 5.1.2 Einfluss der Leistung bei hohen Gasflusswerten 72 5.2 μc-Si:H Schichten und Solarzellen – Frequenzerhöhung 74 5.2.1 μc-Si:H Schichteigenschaften – Vergleich 120 und 140 MHz 74 5.2.2 μc-Si:H Solarzellen – Vergleich 120 und 140 MHz 76 5.3 Weitere Entwicklung der μc-Si:H Solarzellen 78 5.4 Zusammenfassung der Ergebnisse 79 6 Passivierungsschichten für HIT-Solarzellen 81 6.1 Schichteigenschaften – Vergleich zwischen 13,56 und 140 MHz 81 6.2 H2-Plasma-Vorreinigung 84 6.3 Passivierungsschichten – Frequenzeinfluss 87 6.4 Zusammenfassung der Ergebnisse 88 7 Simulationsstudie 89 7.1 Ionenbeschussenergie 89 7.1.1 Modellübersicht – Ar-Plasma 90 7.1.2 Einfluss der Leistung und Betriebsfrequenz 91 7.2 Simulation des Ionenbeschusses 92 7.2.1 TRIM–Simulationssoftware 92 7.2.2 Ionenbeschuss auf die a-Si:H-Oberfläche 93 7.3 Solarzellen – Defekte in der i- Schicht 94 7.3.1 ASA–Simulationssoftware 95 7.3.2 Parameterset 99 7.3.3 Einfluss der Defektdichte auf Solarzelleneigenschaften 101 7.4 Zusammenfassung der Ergebnisse 102 8 Zusammenfassung und Ausblick 105 II. Abbildungsverzeichnis 111 III. Tabellenverzeichnis 117 IV. Literaturverzeichnis 119 V. Veröffentlichungen 129 VI. Lebenslauf 131 VII. Danksagung 133

De nos jours les applications spatiales nécessitent d’embarquer toujours plus d’équipements afin de rendre les missions les plus complètes possibles. Cependant l’espace à bord des satellites est une ressource limitée et par conséquent, la miniaturisation de l’électronique embarquée est une nécessité cruciale. Dans les applications embarquées couvrant plusieurs plages de fréquence différentes, l’utilisation d’antennes ultra large bande (ULB) est une solution classique et efficace pour limiter le nombre d’antennes et de circuits associés. Leur miniaturisation présente donc un enjeu scientifique majeur. Une technique de miniaturisation consistant à charger une antenne spirale d’Archimède par un empilement d’anneaux résonants et couplés a récemment été découverte [1]-[3]. Elle permet une diminution de l’ordre de 35% du diamètre de l’antenne sans dégradation notable des performances en rayonnement. Les travaux de cette thèse permettent d’affiner la compréhension physique du rôle joué par les anneaux dans le phénomène de miniaturisation. Un circuit électrique équivalent est élaboré sur la base d’équations intégrales utilisant des fonctions d’essai étendues et le concept d’impédance de surface réactive. Ce circuit permet de simuler la réponse électromagnétique des anneaux empilés et couplés 10 fois plus vite qu’en utilisant des logiciels de simulation commerciaux et rigoureux. Ce gain de temps est mis à profit pour tester un nombre de combinaisons importants de solutions parmi lesquelles il est possible d’identifier la structure optimale pour la miniaturisation de la spirale d’Archimède chargée par des anneaux empilés et résonants. Pour maximiser l’effet des anneaux résonants couplés dans la miniaturisation de l’antenne, le choix de la fréquence de résonance des anneaux est crucial. Cette fréquence doit être suffisamment basse et permettre à l’antenne de rester adaptée en impédance sur la bande de fréquence la plus large possible. La fréquence de résonance des anneaux dépend du périmètre déployé des anneaux. Ce périmètre est fixé par le choix du motif de base et par le nombre de ses répétitions le long des anneaux. Une méthode rapide pour choisir le motif le plus adapté à la conception de l’antenne miniaturisée est présentée. Cette méthode et le circuit électrique équivalent permettent la conception optimisée et rapide d’une antenne ULB miniature. La validation de cette méthodologie de conception s’est faite expérimentalement sur la base de plusieurs réalisations. / Currently space applications require to embark more and more equipment to make the most complete missions possible. However, the space on satellites is a limited resource, therefore miniaturization of embedded electronics is a crucial requirement. In embedded applications covering several frequency ranges, use Ultra WideBand antennas (UWB) is a classic and effective solution to limiting the number of antennas and associated circuits. Therefore, the miniaturization of UWB antennas is a major scientific challenge. A miniaturization technique was recently discovered [1] - [3]. It consists to load an Archimedean spiral antenna by stacking coupled resonant rings. This technique allows a reduction of about 35% of the diameter of the antenna without significant degradation of radiating performances. The work of this thesis allows to improve the physical understanding of the role played by the rings in the miniaturization process. An equivalent circuit is developed on the basis of integral equations using extended test functions and the concept of surface impedance. This circuit simulates the electromagnetic response of the coupled and stacked rings 10 times faster than using commercial and rigorous simulation software. This time saving is employed to test a large number of solutions from which it is possible to identify the optimal structure for the miniaturization of the Archimedean spiral loaded with stacked resonant rings. To maximize the effect of coupled resonant rings in the miniaturization of the antenna, the choice of the resonant frequency of the rings is essential. This frequency must be low enough and allow the antenna to stay matched over the widest possible frequency band. The resonant frequency of the rings depends on the deployed perimeter of the rings. The perimeter length is fixed by the choice of the pattern and its number of repetitions along the rings. A quick methodology to select the most suitable pattern for the design of the miniaturized antenna is presented. This method and the equivalent electrical circuit enable a quick and optimized design of a miniature UWB antenna. The validation of this design methodology was done experimentally on the basis of several realizations.

Au cours de ces dernières années, les communications sans fil connaissent une croissance vertigineuse, avec le développement de standards de communication de plus en plus nombreux, qui ouvrent la voie à de multiples applications telles que : la téléphonie mobile, le biomédical, le maritime, le civil et le militaire. De nos jours, les communications sans fil se sont diversifiées et multipliées. Cela entraîne la conception d’antennes toujours plus innovantes, performantes et de taille de plus en plus réduite (miniaturisation). Le projet FLEXBEA (FLEXible BEAcon) a pour but le développement d’un nouveau concept de balises de détresse miniatures (AIS et COSPAS-SARSAT), faible coût, intégrées dans des équipements de sécurité maritime tels qu’un radeau de survie et un gilet de sauvetage. Ces équipements sont destinés aux professionnels de la mer et aux plaisanciers. L’atout majeur de ce nouveau concept est l’intégration dans des équipements de sécurité maritime d’une fonction de détresse en cas de problème majeur : homme à la mer (MOB, Man OverBoard) par exemple lors d’un naufrage. Différentes antennes ont été étudiées. Nous présentons des antennes planaires (de type dipôle ou monopôle imprimé) développées dans la bande UHF : une solution de dipôle avec brins repliés est proposée afin de réduire l'encombrement, et deux modes d'alimentation (symétrique / dissymétrique) sont comparés. Des exemples d'antenne monopôle sont ensuite présentés avec une modification de leur géométrie (structures de type Bow-tie ou méandre) pour assurer une miniaturisation optimale. Puis les antennes filaires retenues pour le projet, avec une modélisation de ces antennes par un circuit équivalent (RLC). Des formules analytiques sont proposées afin de déterminer les valeurs de composants RLC qui interviennent dans le modèle circuit. Ensuite, nous sommes passés à la conception de l’antenne de la balise. Deux antennes ont été conçues et mesurées. Un monopôle ruban avec introduction de composants localisés pour la balise AIS et COSPAS-SARSAT, et une antenne hélice fonctionnant dans la bande AIS, intégrée dans la balise "SIMY". De nombreuses réalisations et mesures ont été effectuées pour caractériser ses antennes. / Over the last few years, wireless communications have grown dramatically, with the development of more and more communication standards, which open the way to multiple applications such as: mobile telephony, biomedical, maritime, the civilian and the military. Today, wireless communications have diversified and multiplied. This leads to the design of antennas that are always more innovative, more efficient and smaller in size (miniaturization). The FLEXBEA project (FLEXible BEAcon) aims to develop a new concept of low cost miniature distress beacons (AIS and COSPAS-SARSAT) integrated into marine safety equipment such as a life raft and a lifejacket safety. This equipment is intended for professionals of the sea and boaters. The main advantage of this new concept is the integration in maritime safety equipment of a distress function in case of major problem: man overboard (MOB, Man OverBoard) for example during a shipwreck. Different antennas have been studied. We present planar antennas (dipole type or printed monopoly) developed in the UHF band: a dipole solution with folded strands is proposed to reduce the bulk, and two modes of supply (symmetrical / asymmetrical) are compared. Examples of monopole antennas are then presented with a modification of their geometry (Bow-tie or meander type structures) to ensure optimal miniaturization. Then the wired antennas selected for the project, with a modeling of these antennas by an equivalent circuit (RLC). Analytical formulas are proposed to determine the RLC component values ​​involved in the circuit model. Then we went to the design of the beacon antenna. Two antennas were designed and measured. A ribbon monopoly with introduction of localized components for the AIS and COSPAS-SARSAT beacon, and a helix antenna operating in the AIS band, integrated into the "SIMY" beacon. Many achievements and measurements have been made to characterize its antennas.

[pt] Os efeitos da difração na propagação de ondas de rádio sobre terreno irregular em VHF e outras bandas a ser usado por futuras aplicações da TV digital são normalmente estimados usando um dos muitos modelos clássicos. Nesta dissertação é feita uma comparação dos erros cometidos na previsão do sinal recebido por três modelos de propagação computacionalmente intensivos. Os resultados da presente comparação indicarão se os esforços computacionais envolvidos na aplicação destes métodos são capazes de diminuir o valor médio e desvio padrão das diferenças entre as medidas e predições determinadas pelos métodos clássicos. / [en] Diffraction effects on the propagation of radio wave over irregular terrain in the VHF and other bands to be used by future digital TV applications are normally estimated using one of many classical models. In this dissertation is made a comparison of the errors committed prediction of signal received by three propagation models computationally-intensive. The results of the present comparison will indicate whether the computational efforts involved on the application of these methods are capable of decreasing the mean value and the standard deviation of the difference between measurements and predictions determined by the classical methods.

Thin-film silicon tandem solar cells based on a hydrogenated amorphous silicon (a-Si:H) top-cell and a hydrogenated microcrystalline silicon (μc-Si:H) bottom-cell are a promising photovoltaic technology as they use a combination of absorber materials that is ideally suited for the solar spectrum. Additionally, the involved materials are abundant and non-toxic which is important for the manufacturing and application on a large scale. One of the most important factors for the application of photovoltaic technologies is the cost per watt. There are several ways to reduce this figure: increasing the efficiency of the solar cells, reducing the material consumption and increasing the throughput of the manufacturing equipment. The use of very-high frequencies has been proven to be beneficial for the material quality at high deposition rates thus enabling a high throughput and high solar cell efficiencies. In the present work a scalable very-high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique for state-of-the-art solar cells is developed. Linear plasma sources are applied which facilitate the use of very-high frequencies on large areas without compromising on the homogeneity of the deposition process. The linear plasma sources require a dynamic deposition process with the substrate passing by the electrodes in order to achieve a homogeneous deposition on large areas. State-of-the-art static radio-frequency (RF) PECVD processes are used as a reference in order to assess the potential of a dynamic VHF-PECVD technique for the growth of high-quality a-Si:H and μc-Si:H absorber layers at high rates. In chapter 4 the influence of the deposition process of the μc-Si:H i-layer on the solar cell performance is studied for static deposition processes. It is shown that the correlation between the i-layer growth rate, its crystallinity and the solar cell performance is similar for VHF- and RF-PECVD processes despite the different electrode configurations, excitation frequencies and process regimes. It is found that solar cells incorporating i-layers grown statically using VHF-PECVD processes obtain a state-of-the-art efficiency close to 8 % for growth rates up to 1.4 nm/s compared to 0.53 nm/s for RF-PECVD processes. The influence of dynamic deposition processes on the performance of μc-Si:H solar cells is studied. It is found that μc-Si:H solar cells incorporating dynamically grown i-layers obtain an efficiency of 7.3 % at a deposition rate of 0.95 nm/s. There is a small negative influence of the dynamic deposition process on the solar cell efficiency compared to static deposition processes which is related to the changing growth conditions the substrate encounters during a dynamic i-layer deposition process. The changes in gas composition during a dynamic i-layer deposition process using the linear plasma sources are studied systematically using a static RF-PECVD regime and applying a time-dependent gas composition. The results show that the changes in the gas composition affect the solar cell performance if they exceed a critical level. In chapter 5 dynamic VHF-PECVD processes for a-Si:H are developed in order to investigate the influence of the i-layer growth rate, process parameters and deposition technique on the solar performance and light-induced degradation. The results in this work indicate that a-Si:H solar cells incorporating i-layers grown dynamically by VHF-PECVD using linear plasma sources perform as good and better as solar cells with i-layers grown statically by RF-PECVD at the same deposition rate. State-of-the-art stabilized a-Si:H solar cell efficiencies of 7.6 % are obtained at a growth rate of 0.35 nm/s using dynamic VHF-PECVD processes. It is found that the stabilized efficiency of the a-Si:H solar cells strongly decreases with the i-layer deposition rate. A simplified model is presented that is used to obtain an estimate for the deposition rate dependent efficiency of an a-Si:H/μc-Si:H tandem solar cell based on the photovoltaic parameters of the single-junction solar cells. The aim is to investigate the individual influences of the a-Si:H and μc-Si:H absorber layer deposition rates on the performance of the tandem solar cell. The results show that a high deposition rate of the μc-Si:H absorber layer has a much higher potential for reducing the total deposition time of the absorber layers compared to high deposition rates for the a-Si:H absorber layer. Additionally, it is found that high deposition rates for a-Si:H have a strong negative impact on the tandem solar cell performance while the tandem solar cell efficiency remains almost constant for higher μc-Si:H deposition rates. It is concluded that the deposition rate of the μc-Si:H absorber layer is key to reduce the total deposition time without compromising on the tandem solar cell performance. The developed VHF-PECVD technique using linear plasma sources is capable of meeting this criterion while promoting a path to scale the processes to large substrate areas.